1. Field of the Invention
The invention relates to a wire electric discharge machine, and particularly to a wire electric discharge machine that has a core fixing function of preventing the drop of the core when cutting out the core, by attaching and depositing machining debris to a workpiece and the core, in a part of a machining groove formed by electric discharge machining.
2. Description of the Related Art
In the wire electric discharge machine, a function (hereinafter, referred to as a core fixing function) of attaching and depositing (welding) the machining debris to the machining groove of the workpiece to fix the machined core to the workpiece, by utilizing a attachment phenomenon of the wire component to the workpiece has been known. As the core fixing function, a method of machining a large number of respective generated cores while fixing, and applying an external force to each of the fixed cores after completion of the whole machining to remove the cores from the workpiece has been taken. Since this method is efficient, its effect is exhibited in the machining in which the large number of the cores are generated.
For example, JP 2012-166332 A discloses an invention in which, when a machining shape is machined, in at least one position of the machining shape, instead of a welding cycle from a machining cycle of the electrical machining condition, a part of the wire electrode is melted, the workpiece and the cutout material are welded by a wire electrode melt to prevent detachment of the cutout material, and after completion of the electric discharge machining, the welded portion is destroyed by an external force to separate the cutout material from the workpiece. Further, JP 2014-24132 A discloses a method for editing a machining program for a wire electric discharge machine which analyzes the machining program, calculates a machining circumference length of a cutout machining member and an upper surface area of a shape of the machining member from the workpiece, calculates the mass of the machining member from the obtained machining circumference length, the upper surface area, the thickness of the workpiece and specific gravity, and obtains a length of the welding portion of the machining member to the obtained mass, by a map which stores a relation between the mass of the machining member and the length of the welding portion capable of holding the machining member.
Further, JP 2014-14907 A discloses a wire electric discharge machine and an automatic programming device for the wire electric discharge machine capable of arbitrarily setting a fixing position, when fixing the core to the work base material by attaching and depositing the machining debris to the machining groove.
Further, JP 2013-144335 A also discloses a machining program generating device of a wire electric discharge machine which sets an attachment region for attaching the components of the wire electrode from the shape and the weight of the core and generates a machining program on the basis thereof in order to prevent the drop of the core.
When adopting the method for fixing the core by the aforementioned core fixing function, the core is not always fixed. There was a problem of failure in fixing of the core to the workpiece for some reasons such as errors of various settings, changes in liquid quality of machining liquid, and aging variations of the wire electric discharge machine itself. For example, when a core 6 is not fixed and the core 6 is caught on a nozzle 5a as illustrated in FIG. 5B, if the nozzle 5a is moved in a right direction in such a state, there is a problem of damage to the nozzle 5a and the wire guide unit by interposing the core 6 between the nozzle 5a and the workpiece 3. Naturally, since it is not possible to perform the continuous machining, and repair of the machine is also necessary, a prolonged machine down occurs. Moreover, when a disconnection of the wire electrode occurs during machining, there is also a problem of breakage of the fixing portion at the time of returning to a breaking point after automatic wire connection. Due to this problem, some users of the wire electric discharge machine may not use the core fixing function for fear.